1. Field of the Invention
The present invention relates generally to an extended remote copy operation for data on direct access storage devices, and more particularly, to a system that insures data consistency in an extended remote copy operation without updates.
2. Description of Related Art
Data processing systems typically are required to store large amounts of data. Having a back-up data copy is mandatory for many businesses as data loss could be catastrophic to the business. Moreover, disaster recovery requires that the secondary copy of data be stored at a location remote from the primary data.
A known method of providing disaster protection is to back-up data to tape, on a daily or weekly basis, etc. The tape is then taken to a secure storage area that is usually located remote from the primary data location. A problem is presented in this back-up plan in that it could take days to retrieve the back-up data, and meanwhile several hours or even days of data could be lost, or worst, the storage location could be destroyed by the same disaster.
A somewhat improved back-up method would be to transmit data to a back-up location each night. This allows the data to be stored at a more remote location. Again, some data may be lost between back-ups since back-up does not occur continuously, as in the dual copy solution. Hence, a substantial data amount could be lost which may be unacceptable to some users.
More recently introduced data disaster recovery solutions include extended remote copy operations, wherein data is backed-up not only remotely, but also continuously. In order to communicate duplexed data from one host processor to another host processor, or from one storage controller to another storage controller, or some combination thereof, a substantial amount of control data is required for realizing the process. A high overhead, however, can interfere with a secondary site's ability to keep up with a primary site's processing, thus threatening the ability of the secondary site to be able to recover the primary in the event a disaster occurs.
Accordingly, there is a need in the art for a method managing data consistency in such environments. More specifically, the challenge is how to insure consistency in an environment where heavy updates occur at one point in time and the system can be completely idle at another point in time, and then report the consistency time accurately.